1. Technical Field
The present invention pertains generally to novel Neisseria meningitidis serogroup B glycoconjugates. More particularly, the invention pertains to glycoconjugates formed from a Neisseria meningitidis serogroup B capsular oligosaccharide derivative (MenB OS derivative) in which sialic acid residue N-acetyl groups have been replace with N-acyl groups, and methods of making and using those glycoconjugates.
2. Background of the Invention
Neisseria meningitidis is a causative agent of bacterial meningitis and sepsis. Meningococci are divided into serological groups based on the immunological characteristics of capsular and cell wall antigens. Currently recognized serogroups include A, B, C, D, W-135, X, Y, Z and 29E. The polysaccharides responsible for the serogroup specificity have been purified from several of these groups, including A, B, C, D, W-135 and Y.
N. meningitidis serogroup B (xe2x80x9cMenBxe2x80x9d) accounts for approximately 50 percent of bacterial meningitis in infants and children residing in the U.S. and Europe. The organism also causes fatal sepsis in young adults. In adolescents, experimental MenB vaccines consisting of outer membrane protein (OMP) vesicles have been found to be approximately 50% protective. However, no protection has been observed in vaccinated infants and children, the age groups at greatest risk of disease. Additionally, OMP vaccines are serotype- and subtype-specific, and the dominant MenB strains are subject to both geographic and temporal variation, limiting the usefulness of such vaccines.
Effective capsular polysaccharide-based vaccines have been developed against meningococcal disease caused by serogroups A, C, Y and W135. However, similar attempts to develop a MenB polysaccharide vaccine have failed due to the poor immunogenicity of the capsular MenB polysaccharide (termed xe2x80x9cMenB PSxe2x80x9d herein). MenB PS is a homopolymer of (N-acetyl (xcex12xe2x86x928) neuraminic acid. Escherichia coli K1 has the identical capsular polysaccharide. Antibodies elicited by MenB PS cross-react with host polysialic acid (PSA). PSA is abundantly expressed in fetal and newborn tissue, especially on neural cell adhesion molecules (xe2x80x9cNCAMsxe2x80x9d) found in brain tissue. PSA is also found to a lesser extent in adult tissues including in kidney, heart and the olfactory nerve. Thus, most anti-MenB PS antibodies are also autoantibodies. Such antibodies therefore have the potential to adversely affect fetal development, or to lead to autoimmune disease.
MenB PS derivatives have been prepared in an attempt to circumvent the poor immunogenicity of MenB PS. For example, C4-C8 N-acyl-substituted MenB PS derivatives have been described. See, EP Publication No. 504,202 B, to Jennings et al. Similarly, U.S. Pat. No. 4,727,136 to Jennings et al. describes an N-propionylated MenB PS molecule, termed xe2x80x9cNPr-MenB PSxe2x80x9d herein. Mice immunized with NPr-MenB PS glycoconjugates were reported to elicit high titers of IgG antibodies. Jennings et al. (1986) J. Immunol. 137:1708. In rabbits, two distinct populations of antibodies, purportedly associated with two different epitopes, one shared by native MenB PS and one unshared, were produced using the derivative. Bactericidal activity was found in the antibody population that did not cross react with MenB PS. Jennings et al. (1987) J. Exp. Med. 165:1207. The identity of the bacterial surface epitope(s) reacting with the protective antibodies elicited by this conjugate remains unknown.
Although the above-described MenB PS derivatives are capable of eliciting a significant anti-MenB PS response, responding antibodies still include a significant proportion of molecules that are cross-reactive with polysialic acid residues in host tissue, and therefore autoreactive. Thus, to date, no approach which has been taken with respect to MenB vaccine development has been successful in providing a safe and effective vaccine against MenB. Accordingly, there remains a need to provide MenB immunogens which can be used in vaccine formulations, wherein the immunogens do not elicit the production of antibodies in immunized animals that are cross-reactive with host tissue and can be thus used in the prevention or treatment of MenB disease.
The present invention is based on the discovery that a substantially homogenous preparation of MenB oligosaccharide (MenB OS) derivative fragments, and glycoconjugates made from those fragments, provide highly effective immunogens for use in anti-MenB vaccine preparations. Antibodies elicited in immunized animals by these MenB OS derivative fragments do not substantially cross-react with host tissue as determined using several binding assays described herein, and are therefore not autoreactive. Since the present MenB OS fragments do not elicit the formation of autoreactive molecules, they provide a safe and efficacious vaccine component for use in the prevention of MenB and E. coli K1 disease.
Accordingly, in one embodiment, the subject invention is directed to a glycoconjugate comprising a MenB OS derivative having sialic acid residue N-acetyl groups replaced with N-acyl groups, wherein the MenB OS derivative is covalently attached to a carrier molecule and has an average degree of polymerization (Dp) of about 10 to about 20.
In another embodiment, the subject invention is directed to a glycoconjugate comprising a MenB OS derivative having sialic acid residue N-acetyl groups replaced with N-propionyl groups, wherein the MenB OS derivative is covalently attached to a tetanus toxoid protein carrier and has an average Dp of about 12 to about 18.
In yet another embodiment, the invention is directed to a method for producing a glycoconjugate comprising:
(a) providing a heterogenous population of MenB OS derivatives wherein sialic acid residue N-acetyl groups have been replaced with N-acyl groups;
(b) obtaining a substantially homogenous group of MenB OS derivatives from the population of (a) wherein the MenB OS derivatives have an average Dp of about 10 to 20;
(c) introducing a reactive group at a nonreducing end of the derivatives obtained in step (b) to provide single end-activated MenB OS derivatives; and
(d) covalently attaching the end-activated MenB OS derivatives to a carrier molecule to provide a MenB OS glycoconjugate comprising substantially homogenous sized MenB OS moieties.
In still a further embodiment, the invention is directed to a method for producing a glycoconjugate comprising:
(a) providing a heterogenous population of MenB OS derivatives wherein sialic acid residue N-acetyl groups have been replaced with N-propionyl groups;
(b) obtaining a substantially homogenous group of MenB OS derivatives from the population of (a) wherein the MenB OS derivatives have an average Dp of about 12 to 18;
(c) introducing a reactive group at a nonreducing end of the derivatives obtained in step (b) to provide single end-activated MenB OS derivatives; and
(d) covalently attaching the end-activated MenB OS derivatives to a tetanus toxoid carrier molecule to provide a MenB OS/tetanus toxoid glycoconjugate comprising substantially homogenous sized MenB OS moieties.
In still further embodiments, the subject invention relates to glycoconjugates produced by these methods, to vaccine compositions comprising the glycoconjugates in combination with a pharmaceutically acceptable excipient, and to methods of forming the vaccine compositions.
In another embodiment, the subject invention is directed to a method for preventing or treating MenB and/or E. coli K1 disease in a mammalian subject comprising administering a therapeutically effective amount of the above vaccine compositions to the subject.
These and other embodiments of the present invention will readily occur to those of ordinary skill in the art in view of the disclosure herein.